Method to reject disk drive disturbance

Abstract

Track mis-registration (TMR) correction is conditionally made in a hard disk drive using servo data in a closed loop servo control scheme, along with one or more alternative sensing schemes when an external shock or vibration occurs. The alternative sensing schemes include measurement of spindle motor speed using a frequency of servo markers read from a rotating disk, voice control motor (VCM) back emf, spindle motor speed back emf, and accelerometer readings. The predicted TMR resulting from the signal generated by the alternative sensing scheme(s) is simulated based upon a model of the disk drive system, and corrections are applied only if the expected TMR due to the disturbances is large enough that application of the corrections using the alternative sensing scheme would be likely to reduce the overall TMR. In one case, actual operation is occasionally performed with and without corrective TMR feedback from the selected sensing scheme(s), and the actual values are compared with predictions from the system model and the results are used to update the system model.

1. A method used by a servo system for a hard disk drive to control the track alignment of a transducer head relative to a desired tracking location comprising:
 measuring track alignment using servo data position error signals (PES) read from a rotatable disk by the read head; 
 measuring a feed forward signal indicative of external disturbances applied to the hard disk drive; and 
 determining track alignment using the PES measurement and the feed forward signal measurement, the feed forward signal measurement being used to determine corrections only when the servo system determines use of the feed forward signal reduces track alignment error, wherein the servo system determines that use of the feed forward signal will likely reduce the track alignment error when a threshold is exceeded, the threshold being set with a magnitude so that moving the read/write head to make correct track alignment corrections after the disturbance occurs would take less time than use of the PES alone. 
 
   
   
     2. The method of  claim 1 , wherein the feed forward signal comprises a spindle motor speed indication determined from a frequency of servo markers passing the transducer head. 
   
   
     3. The method of  claim 1 , wherein the feed forward signal comprises a signal from an accelerometer. 
   
   
     4. The method of  claim 1 , wherein the feed forward signal comprises a back electro-motive force (emf) signal from a VCM. 
   
   
     5. The method of  claim 1 , wherein the feed forward signal comprises a back electro-motive force (emf) signal from a spindle motor. 
   
   
     6. The method of  claim 1 , wherein the servo system determines that use of the feed forward signal will reduce the track alignment error when a threshold is exceeded, the threshold being determined from a computer model enabling comparison of a predicted PBS amount with and without use of the feed forward signal. 
   
   
     7. The method of  claim 1 , wherein when the feed forward measurement is used, track alignment correction is provided using the feed forward signal without the PES signal. 
   
   
     8. The method of  claim 1 , wherein when the feed forward measurement is used, track alignment correction is provided using both the feed forward signal and the PES signal. 
   
   
     9. A method used by a servo system for a hard disk drive to control the track alignment of a read head relative to a desired tracking location comprising:
 measuring track alignment using servo data position error signals (PES) read from a rotatable disk by the read head; 
 measuring a feed forward signal indicative of external disturbances applied to the hard disk drive; and 
 determining the track alignment using the PES measurement and the feed forward signal measurement, the feed forward signal measurement being used to determine the track alignment only when a threshold value related to the disturbance is detected, wherein the threshold value is provided with hysteresis so that the threshold has a first value when use is made of the feed forward measurement and second value when switching back to not using the feed forward measurement. 
 
   
   
     10. The method of  claim 9 , wherein the threshold value comprises a PBS signal magnitude. 
   
   
     11. The method of  claim 9 , wherein the threshold value comprises a disturbance magnitude. 
   
   
     12. A method used by a servo system for a hard disk drive to control the track alignment of a transducer head relative to a desired tracking location comprising:
 measuring track alignment using servo data position error signals (PES) read from the rotatable disk by the transducer head; 
 measuring a feed forward signal indicative of a disturbance applied to the hard disk drive; and 
 determining track alignment corrections using the PES measurement and the feed forward signal measurement, the feed forward signal measurement being used to control corrections only when there is a determination that use of the feed forward signal measurement reduces track alignment error, wherein when the feed forward signal measurement is used, track alignment correction is provided using the feed forward signal without the PES signal. 
 
   
   
     13. In a method used by a servo system for a hard disk drive that controls track alignment of a transducer head relative to a desired track using a first measurement made from servo data position error signals (PBS) read from a rotatable disk by the transducer, the improvement comprising:
 using a second measurement made from a feed forward signal indicative of a disturbance applied to the hard disk drive to control the track alignment only when there is a determination that use of the second measurement reduces track alignment error, wherein the determination is made that use of the feed forward signal will likely reduce the track alignment error when a threshold is exceeded, the threshold being set with a magnitude so that moving the read/write head to make correct track alignment corrections after the disturbance occurs would take less time than use of the PES alone.